This invention relates to the production of polymers of ethylene. In one of its aspects this invention relates to the activation of chromium-containing catalysts. In another of its aspects this invention relates to the activation of chromium-containing catalysts suitable for use in the production of polymers of ethylene.
Supported chromium oxide catalysts can be used to prepare olefin polymers in a hydrocarbon solution. These catalysts can also be used to prepare olefin polymers in a slurry system in which the polymers are produced in the form of small particles of solid materials suspended in a diluent. This second process, usually referred to as a particle-form process, has the advantage of being less complex than the solution polymerization process. Control of certain characteristics of polymer is considerably more difficult in the particle-form process than in the solution process. For instance, in the solution process, it is known that a lower molecular weight (higher melt flow) polymer is produced as the polymerization temperature is increased. In the slurry process, however, any effort to increase the melt flow to an appreciable extent by increasing temperature causes the polymer to go into solution so that there is no longer a slurry and the basic concept of slurry or particle-form process is destroyed.
It is, therefore, of great interest to provide a method by which melt index control can be effected in polymerization processes, particularly when the method is applicable to such varying polymerization processes as gas phase, solution polymerization, and particle-form polymerization.
It is therefore an object of this invention to provide a catalyst capable of providing polymers of ethylene having a high melt index. It is another object of this invention to provide a catalyst suitable for use in slurry polymerization systems. It is another object of this invention to provide a method for activating a chromium-containing catalyst. It is another object of this invention to provide a catalyst capable of giving good activity and also producing polymer of high melt index.
Other aspects, objects and the various advantages of this invention will become apparent upon reading this specification and the appended claims.